In Release-8 version of LTE (Long Term Evolution), it is defined that CRS (Common Reference Signal) common among cells is transmitted in a downlink.
The CRS is used for the measurement of mobility or the measurement of channel quality information (CQI: Channel Quality Indicator) in a mobile station UE, in addition to a demodulation process of downlink data.
Furthermore, in LTE Release-10 version, it is defined that CSI-RS (Channel State Information-Reference Signal) common among cells and dedicated for CQI measurement is transmitted in addition to the CRS.
Moreover, in the LTE Release-10 version, for the improvement of the accuracy of channel estimation between neighboring cells through the CSI-RS, in order that the CSI-RS and a downlink data channel (PDSCH: Physical Downlink Shared Channel) are not collided between the neighboring cells, it is defined to use a scheme (that is, Muting) for performing scheduling in which the PDSCH of the neighboring cell is not assigned to a subframe for transmitting the CSI-RS.
Furthermore, it is discussed that a radio base station eNB notifies a mobile station UE of “CSI-RS/Muting configuration information” indicating a transmission method (for example, a pattern, a cycle, or a subframe offset value of CSI-RS/Muting) of the above-described CSI-RS.